For instance, a connector disclosed in PTL1 includes an insulative connector housing, an insulative spacer and an electrically conductive terminal fitting. The connector housing includes a terminal accommodating chamber and a spacer fitting part communicating with the terminal accommodating chamber. A lance having flexibility is integrally formed in the terminal accommodating chamber. When the terminal fitting is inserted into the terminal accommodating chamber by a prescribed amount while bending the lance, the bent lance is restored to an original state and is engaged with the terminal fitting. Further, when the spacer is fitted to the spacer fitting part, the terminal fitting is double engaged with the spacer. When the spacer is not fitted to the spacer fitting part, it is detected that the terminal fitting is in a half inserted state.